Beware the Three Headed Monster

 In North American railroad Signaling truly "universal" rules are pretty rare as in almost every situation one can usually find exceptions.  For having a high green reserved exclusively for Clear is pretty universal except the Bessemer and Lake Erie uses G/*Y* for Approach Limited and G/Y for Limited Clear.  Well another one of these rules is that intermediate signals either have one or two heads. By intermediate signals I am referring to signals with a number plate or signals with offset heads that cannot display an absolute Stop indication. Well there is one big exception to this and it is the Y/R/G Approach Slow indication used by a number of Conrail predecessors like the New York Central and Reading Systems and, more recently, CSX via the Seaboard System. 

 

This results in what I like to call a "three headed monster" in that you have an exceptionally tall intermediate signal that makes one question if they are at an interlocking or not.  Although potentially less of an issue due to PTC, salience is a huge human factors issue and when designing a signaling system from scratch like Caltrain did, making every absolute signal three heads, every automatic distant signals two heads and every basic block signal one head makes it harder for the engineer to become confused about what sort of signal is coming up. The Y/R/G three headed monster sort of blows this approach out of the water, but fortunately Approach Slow is one of the less commonly encountered indications. 

However if one is able to look past the signal policy issues and get into the fun world of rare signaling setups, CSX's three headed monster as a few additional tricks up its sleeve. If an interlocking has both slow and Medium/Limited Speed then you get a 7 lamp, 3 head intermediate signal (GYR-GR-GR) like the ones at Milepost 70 west of Point of Rocks.

 Alright, but I think we can do even better!  What if we had a situation with both Slow and Medium Speed routes AND short signal blocks between that next interlocking and one after.  Well, then we'd have an 8 lamp, 3 head intermediate signal (GYR-GYR-GR) and thanks to some recent capacity expansion and re-signaling work an example now exists in the Richmond area on the Belt Line just west of AY wye.

Don't forget, if CSX had simply adopted the NORAC style signal rules with Y/Y Approach Slow and *Y* Advance Approach they would have been able to do this with 6 lamps and 2 heads, but thanks to their Dixieland myopia we now have what is probably the ultimate intermediate signal. The fact that the masts are on both tracks is even better, 

 
Before I go I would like to mention that there is another three headed intermediate signal still in use and that would be Y/Y/G Approach Diverging on Kansas City Southern. Some newer materials are showing the use of Y/Y and with all the recent re-signaling I am unsure if any Y/Y/G still survives, but it technically could exist. Also, in case anyone was wondering if Canada and its crazy quilt of signal indications has a three headed intermediate, they do not as the indication chart would show it with offset heads and all offset head indications have at most two heads. 

Anyway, if I missed anything or you know other examples of an ultimate intermediate signal location please let me know in the comments.